To monitor output power of a power amplifier, the input of a power detector typically is connected to the output of the power amplifier. That is, the input power of the power detector is the output power of the power amplifier. Recently, however, the input of the power detector is connected to an intermediate stage of the power amplifier. This approach may avoid the influence from mismatch of an antenna coupled to the output of the power amplifier, but the detected power is not the actual output power of the power amplifier. Furthermore, the output power of the power amplifier varies with temperature.